Method and apparatus for finishing turbine blades



Jan. 17, 1956 c, SCHQRNER 2,730,794

METHOD AND APPARATUS FOR FINISHING TURBINE BLADES Filed July 17, 1.951

Fig. 1.

INVENTOIZ,

CHRISTIAN Scnb'wea BY WKWMM ATTORNEYS United States Patent METHOD ANDAPPARATUS FOR FINISHING TURBINE BLADES Christian Schorner, Augsburg,Germany, assignor to Maschinenfabrilr Augsbnrg-Niirnberg A. G.,Augsburg, Germany, a corporation of Germany Application July 17, 1951,Serial No. 237,228

Claims priority, application Germany lanuary 20, 1951 13 (Zlairns. (Cl.29-156.8)

This invention relates to a method and apparatus for aligning andmachining sets of ceramic blades for turbine rotors.

The tight fit of the ceramic blades in the annular groove of the steelrotor is an important requirement for a reliable fixing of the bladeswhich are exposed to very exacting conditions of operation. Specialmeasures are required to take care of the different specific thermalexpansions of the assembled constructional materials. In view of thevariations occurring in constructional elements of ceramic materialowing to the shrinking in the firing operation, depending on theirstructure, composition, shape etc., it is difricult to ensure therequisite uniformity among the blades of a set of blades with reasonableexpenditure, especially in case of series production.

Therefore, it is preferred to machine the seating surfaces of the bladesby grinding them in an assembled condition of the complete set ofblades. In assembling the blades, all possible causes of injuries of thebrittle constructional elements of ceramic material must be strictlyprecluded, the more so as such injuries while oftentimes being difiicultto ascertain, even with the test methods used for testing steel, wouldtend to cause troubles in operation.

It is an object of the present invention to provide methods and meansfor assembling the blades into a selfcontained unit for machining theseating surfaces and the tips of the blades, in such a way thatmechanical injuries of the blades are strictly avoided.

With this and further objects in view, according to the presentinvention the blades are aligned in a dummy having an annular groovecorresponding to the annular groove of the rotor, and the blade gridregion is filled up, within a sectional cage centered on the dummy, witha compound mass melting at moderate temperatures. After the aligning ofthe blades in the dummy groove and the fitting in of the filling massinto the blade grid the existing gaps, irregularities, cavities etc. onthe seating surfaces of the blades are equalized by filling in a thinlyliquid, self-hardening deposit mass, e. g. a ceramic mass or cement. Onremoval of the dummy the cage with the blade rim embedded therein isused as a centered holder for machining the root of the blades. Finally,on removal of the cage and fitting of the blade rim in the turbine rotorthe compound mass serves to hold and support the blades when grindingtheir tips.

It has been found that ceramic blades aligned and machined in this wayensure faultless running characteristics of the turbine rotor.

Other and further objects, features and advantages of the invention willbe pointed out hereinafter and appear in the appended claims formingpart of the application.

In the accompanying drawings a now preferred embodiment of the invenionis shown by way of illustration and not by way of limitation.

, Fig. 1 is an axial section through a device for carrying out theinvention, including the dummy rotor with the blades inserted in thegroove thereof, and the casting cage,

Fig. 2 is a similar section, but showing only the casting cage with theblades embedded therein, with the dummy rotor removed, and

Fig. 3 is a section through he turbine rotor with the blade rim insertedtherein.

Similar reference numerals denote similar parts in the different views.

Referring now to the drawing in greater detail, and first to Fig, 1, itwill be seen that the root portions 11 of the fired ceramic blades 1 areinserted in a bi-partite dummy rotor 2a, 2b with the blade portions 12thereof protruding radially outwardly. The contours of the annulargroove of the dummy 2a, 2b especially as regards the seating surfaces ofthe roots ll of the blades correspond exactly to the correspondingcontours of the actual turbine rotor 3, see Fig. 3. The projectingoperating portions 12 of the blades 1 are encased in a bipartite cage4a, 4b concentrically engaging the dummy 2a, 2b which is mounted on atable 5, by means of a roller bearing 6, so as to be easily rotatable bymeans of shaft it The two halves 2a, 2b of the dummy rotor arereleasably held together as by bolts 13, while the two halves of thecage 4a, 4b are releasably interconnected as by bolts 14.

In order that the blades 1 may be inserted in a position ensuringoptimum stressing conditions in operation, i. e., in such a way that thecenters of gravity of the successive cross sections of each blade ifpossible come to lie along a common radial line, the dummy is rotated ata. pcripheral speed which is rated so that the blades are able to setthemselves into the correct position, thereby effecting alignment ofsaid blades under centrifugal force. This is important because in spiteof the use of negative supports, deformations of the thin portions ofthe blade may occur in firing the blades and it is desirable to reduceas much as possible the deleterious effect upon the stresses inoperation caused thereby.

in blade welding devices for grid rings of steel, special measures forensuring an accurate pitch are usually ap plied. Such measures, however,in most instances require very accurate dimensions of the profile of theblades and, therefore, it is preferred in connection with the methodaccording to the present invention to apply such measures only toachieve a uniform distribution of the blades on the circumference of theset of blades but not in regard to the alignment of the blades, since incase of ceramic material deviations must be expected even in case of anabsolutely uniform treatment in the producion. It is also important toapply only thin and uni form additional layers on the seating surfacesof the root part for the purpose of corrections; therefore, it is notadvisable to adjust the blades according to the position of theiroperative portions. it depends on the shape of the grid or of the rootof the blade or of the additional elements for positive engagement ofthe root independently of the temperature, which point of the blade willbe relied upon for said one-time positioning of the blade pitch orspacing. However, this is of an inferior importance for the presentinvention. In order to facilitate adjustment of the blades according tothe radial direction it is preferred to support the seating surfaces ofthe root portions on slightly projecting points which are provided foreach blade on a line passing through the root cross section, on the twohalves of the dummy. On the right hand side of Fig. l the points 9 forsupporting the roots of the blades are indicated in the seating surfacesof the dummy halves 2a, 2b. Once the blades 1 are thus aligned in theannular groove of the dummy, the grid region is filled up with acompound 7 adapted in the upper half 4a of the bipartite cage.

, 3 to be removed later by melting at a moderate temperature. Theproperties of this compound should be such that it absolutely preservesits shape at normal working temperatures and also duringthe machiningofthe set of blades. This is supported bythe metal cage 41:, lb

which also serves as a holder for the machining since it is coaxial withthe dummy. The meltable compound 7 is introduced among and around theblade vanes 12 by pouring through a plurality of openings 15 providedSuch pouring may conveniently be facilitated by providing a circular damor weir 16.

On solidification of the compound either the dummy is removed forapplying a'suitable metal layer onthe sea ing surfaces of the roots ofthe blades, which metal layer is then machined according to the desiredcontour of the annular groove of the rotor, or the dummy'is directlyused as an accurate mould for application of a cast-on material of aceramic or cement-like nature. This mass may be composed in such a waythat it will harden at room temperature without burning, compensatingall existing irregularities. It is also possible that in specialinstances for obtaining the required mechanical strength of the cast-onmaterial a kind of glazing firing or glaze baking has to be inserted. Tothis end of course, the grid compound mass has to be removed by meltingand recast into the device afterwards for the further machining.Moreover, it is also possible to apply a metal coating additionally onthis compensating layer. Where it is intended to grind the seatingsurfaces thus produced, the contours of the dummy may have slightlyexcessive dimensions. The cast-on mass should be adapted to be cast in aliquid state and set by itself. An unexceptional slip consistency isdesirable in order that all gaps in the seating groove are also filledup by the centrifuging action in the casting operation. It will beunderstood that care has to be taken to specially prepare the dummysurfaces which have to be detached from the compound after themachining. Scaling of the thin deposit layer on incorporation of the setof blades in the turbine rotor has to be strictly prevented, since inoperation at high temperatures the positive engagement of the surfaceswhile being maintained in the meridian plane by the special contours ofthe annular groove, is not preserved in the peripheral direction whereon the contrary gaps will occur between the adjacent roots of the rim ofblades. Therefore, careful insulation of the contact surfaces betweenadjacent blade roots is advisable so as to prevent their growingtogether with the compound mass.

When the machining of the seating surfaces of the blades is finished,the set of blades together with the compound mass in the grid range isfitted in the turbine rotor. The supporting members 8, Fig. 3, arelikewise fitted on the inner side of the root of the blades so as tosecure the blades tightly in their normal position in the rotor forfurther machining of the blades. Now, the tips of the blades are groundto their accurate outside diameter, on removal of the cage 4a, 4b. Sincethe blades are fixedly embedded in the compound, this grinding processwill take place without shocks and impacts, so that the danger ofbreakage during the grinding of the outside diameter of the blade tipsis eliminated.

Finally the compound is melted out at a relatively low temperature andthe rotor with the rim of ceramic blades on balancing is ready to befitted in the turbine. The method according to the invention permits aquick and accurate machining of the ceramic blades, avoiding waste as aresult of their high sensibility to impacts and shocks.

While the invention has been described in detail with respect to a nowpreferred example and embodiment of the invention it will be understoodby those skilled in the art after understanding the invention thatvarious 4 intended, therefore, to cover all such changes andmodifications in the appended claims.

What is claimed is:

1. in a method of imparting uniform close tolerance finishing andfitting to a plurality of nonuniform turbine blades adapted to becarried around the rim of a turbine rotor, the steps which comprisefitting a portion of each said blade into a rotor dummy, spinning saidrotor dummy and said blades effecting automatic alignment of said bladesunder the action of centrifugal forces thereon, fastening togetherportions of said blades outside said dummy into a rigid blade unit whilemaintaining said alignment'of said blades in said rotor dummy, shapingsaid blades into said close tolerance while all said blades are fastenedtogether in aligned position in said unit, and thereafter mounting saidblades in a rotor.

2. In a method of imparting uniform close tolerance finishing andfitting to a plurality of nonuniform turbine blades adapted to becarried in an annular groove around the rim of a turbine rotor, thesteps which comprise fitting a portion of each said blade into a rotordummy having an annular groove substantially equivalent to said groovein said turbine rotor, spinning said rotor dummy and said bladeseifecting alignment of said blades under the action of centrifugalforces thereon, filling hollow spaces between said aligned blades with ahardenable plastic binding material, effecting hardening of saidmaterial forming said aligned blades into a rigid .blade unit, finallyshaping said blades uniformly to said close-tolerance while said bladesare bound together as said unit, removing said rotor dummy from saidblades, and thereafter removing said binding material from said bladesto form said plurality of separate blades each with said uniform closetolerance finishing and fitting.

3. In a method of imparting uniform close tolerance finishing andfitting to a plurality of nonuniform turbine blades includingrootportions adapted to be carriedin an annular groove around the rim ofa turbine rotor, the steps which comprise fitting said root portionsinto a rotor dummy having an annular groove substantially equivalent tosaid groove in said turbine rotor, spinning said rotor dummy and saidblades effecting automatic alignmentof said blades under the action ofcentrifugal forces thereon, filling hollow spaces between said alignedblades with a hardenable plastic binding material forming said bladesinto a rigid blade unit, removing said rotor dummy from said rootportions, uniformly finishing'all said root portions while in said rigidunit imparting uniformly thereto said close tolerance fitting, andthereafter removing said binding material. e

4. In the method of imparting uniform close tolerance finishing andfitting to a plurality of nonuniform turbine blades including rootportions adapted to be carried in an annulargroove around the rim of aturbine rotor, the steps'which'comprise inserting said root portions ofsaid blades into a rotor dummy having an annular groove substantiallyequivalent to said groove in said turbine rotor, spinning said rotordummy and said blades elfecting alignment of said blades under theaction of centrifugal forces thereon, filling hollow spaces between saidaligned blades with a hardenable plastic binding material forming saidblades into a rigid blade unit, introducing into said V groove in saidrotor dummy a fluid ceramic coating material for imparting to all saidfoot portions said uniform close tolerance fit corresponding to saidgroove in said rotor dummy, removing said rotor dummy from said rootportions, and thereafter removing said binding material.

5. In the method of. imparting uniform close tolerance finishing andfitting to a plurality of nonuniform turbine blades including rootportions adapted to be carried in an annular groove aroundthe rim of aturbine rotor, the steps which comprise inserting said root portions ofsaid blades into a rotor dummy'having an annular groovesubstantiallyequivalent to said groove in said turbine rotor, spinningsaid rotor dummy and said blades effecting automatic alignment of saidblades under the action of centrifugal forces thereon, filling hollowspaces between said aligned blades with a hardenable plastic bindingmaterial forming said blades into a rigid blade unit, removing saidrotor dummy from said root portions, machining root portions of all saidblades in said unit to impart uniformly thereto said close tolerancefitting, and thereafter removing said binding material.

6. In the method of imparting uniform close tolerance finishing andfitting to a plurality of nonuniform turbine blades including rootportions adapted to be carried in an annular groove around the rim of aturbine rotor, the steps which comprise inserting said root portions ofsaid blades into a rotor dummy having an annular groove substantiallyequivalent to said groove in said turbine rotor, spinning said rotordummy and said blades effecting alignment of said blades under theaction of centrifugal forces thereon, filling hollow spaces between saidaligned blades with a hardenable plastic binding material forming saidblades into a rigid blade unit, removing said rotor dummy from said rootportions, depositing on said root portions a machineable coating layer,machining root portions of all said blades in said unit to impartuniformly thereto said close tolerance, and thereafter removing saidbinding material.

7. In a method of imparting uniform close tolerance finishing andfitting to a plurality of nonuniform turbine blades including rootportions adapted to be carried in an annular groove around the rim of aturbine rotor, the steps which comprise inserting said root portions ofsaid blades into a rotor dummy having an annular groove substantiallyequivalent to said groove in said turbine rotor, spinning said rotordummy and said blades effecting automatic alignment of said blades underthe action of centrifugal forces thereon, enclosing radially outerportions of said blades in a casing while maintaining said alignment ofsaid blades in said rotor dummy, filling hollow spaces between saidblades in said casing with a hardenable plastic binding material formingsaid blades into a rigid blade unit, removing said rotor dummy from saidroot portions, uniformly finishing all said root portions while in saidrigid unit imparting thereto said close tolerance, removing said casing,uniformly finishing radially outer portions of all said blades while insaid rigid unit imparting uniformly thereto said close tolerance, andthereafter removing said binding material.

8. In a method of imparting uniform close tolerance finishing andfitting to a plurality of nonuniform turbine blades including rootportions adapted to be carried in an annular groove around the rim of aturbine rotor, the steps which comprise inserting said root portions ofsaid blades into a rotor dummy having an annular groove substantiallyequivalent to said groove in said turbine rotor, spinning said rotordummy and said blades effecting automatic alignment of said blades underthe action of centrifugal forces thereon, enclosing radially outerportions of said blades in a casing while maintaining said alignment ofsaid blades in said rotor dummy, filling hollow spaces between saidblades in said casing with a meltable plastic binding material formingsaid aligned blades into a rigid blade unit, removing said rotor dummyfrom said blades, machining root portions of all said blades in saidunit to impart uniformly thereto said close tolerance fitting, removingsaid casing, machining radially outer portions of all said blades insaid unit to impart uniformly thereto said close tolerance fitting, andthereafter melting away said binding material.

9. The method of imparting uniform close tolerance finishing and fittingto a plurality of nonuniform turbine blades adapted to be carried aroundthe rim of a turbine rotor with root portions of said blades inserted inan annular groove in said turbine rotor, which comprises the steps ofinserting root portions of said blades into a rotor dummy having anannular groove substantially dimensionally equivalent to said annulargroove in said turbine rotor, spinning said rotor dummy and said bladesat a predetermined speed effecting alignment of said blades under theaction of centrifugal forces thereon, enclosing radially outer portionsof said blades in a casing while maintaining said alignment of saidblades in said rotor dummy, filling hollow spaces between said blades insaid casing with a hardenable plastic binding material, effectinghardening of said material for firm clamping of said blades in saidaligned position, removing said rotor dummy from said blades whilemaintaining blades aligned in said casing, depositing a mechineablecoating on said root portions of said blades while aligned, machiningroot portions of all said blades to said uniform close tolerance fitwhile all said blades are bound as a unit in said casing, mounting saidblades in a turbine rotor, removing said casing, machining radiallyouter ends of said blades to said uniform close tolerance fit, andmelting away said binding material while maintaining said alignment andclose tolerance finishing and fitting characteristics imparted to saidblades.

10. In apparatus for imparting uniform close tolerance finishing andfitting to a plurality of nonuniform turbine blades adapted to becarried in an annular groove around the rim of a turbine rotor, thecombination which comprises a rotor dummy, rim portions on said dummydefining an annular groove substantially equivalent to said annulargroove in said turbine rotor, means for receiving and retaining saidturbine blades in said rotor dummy annular groove, means for spinningsaid rotor dummy effecting automatic alignment under centrifugal forceof turbine blades inserted into said groove, and means for releasing allsaid blades from said groove while maintaining said aligned condition ofsaid blades,

11. In apparatus for imparting uniform. close tolerance finishing andfitting to a plurality of nonuniform turbine blades including rootportions adapted to be carried in an annular groove around the rim of aturbine rotor, the combination which comprises a rotor dummy, rimportions on said dummy defining an annular groove substantiallyequivalent to said annular groove in said turbine rotor, means forreceiving and retaining said root portions of said blades in said rotordummy annular groove, means for spinning said rotor dummy effectingalignment of said blades inserted into said groove, means for fasteningradially outer portions of said aligned blades to form a rigid bladeunit, and means for releasing all said blades from said dummy whilemaintaining said aligned condition of said blades in said rigid unit.

12. In apparatus for imparting uniform close tolerance finishing andfitting to a plurality of nonuniform turbine blades including rootportions adapted to be carried in an annular groove around the rim of aturbine rotor, the combination which comprises a rotor dummy, rimportions on said dummy defining an annular groove substantiallyequivalent to said annular groove in said turbine rotor, means forreceiving and retaining said root portions of said blades in said rotordummy annular groove, means for spinning said rotor dummy effectingalignment of said blades inserted into said groove, a casing for enclosing radially outward portions of said aligned blades in said dummy,means in said casing for receiving a hardenable plastic binding materialbetween said blades forming said aligned blades into a rigid blade unit,means for releasing all said blades from said groove in said dummy whilemaintaining said alignment of said blades in said rigid unit, and meansfor releasing said casing from said rigid blade unit while maintainingsaid alignment of said blades.

13. In apparatus for imparting uniform close tolerance finishing andfitting to a plurality of nonuniform turbine blades adapted to becarried in an annular groove around the rim of a turbine rotor, thecombination which comprises a pair of substantially circular dummy rotoreleifi'efits, meansfor releasably aflixing Said eleinnts t0- g'ether insubstantially coaxial'alignment, rim ortions 'oneaCh of-sa'id dummyelements mutually defining an 'ilinig Said 'd'fim'my rotorandsaid-blades effecting alignment of'sa'id blades 'u'nder centrifugalforce, and means separate from said d'uminy rotor for retaining saidblades in said aligned condition upon separation of said d'ufnmyelementsfrom said blades.

-Referenc'es Cited in the file of this patent UNITED STATES PATENTS585,696 Player July 6, 1897 Steenstrup Oct. 9, 1923 SteejnStr'uP Aug.25, 19-25 McCall Jan. 26, 1926 Hodgkinson June 5, 1928 Wahlstn Jline 27,1933 Lysholm June 27, 1933 Smith 1 Nov. 17, 1936 Rubissow -J-uly 16,1940 Dodge Oct. 30, Rockwell Mar. 30, 1948, Cronstedt Aug. 16, 1949Eastman July 3, 1951 FOREIGN PATENTS France Oct. 30, 1939

